The correction of refractive errors of the eye by the attachment of donor material directly onto the corneal surface has been carried out in the prior art for several years. The most accepted technique is known as "epikeratophakia". This technique involves the formation of a ring-shaped trough in the recipient corneal bed, and the placement and suturing of the donor material onto the optical center of the cornea with its edges fitting into the trough. This technique requires that the epithelium of the cornea grow over the resulting lenticule which attaches itself to the surface of the lenticule.
Another prior art procedure for refractive correction of the eye is a technique referred to as "intralamellar insertion". This latter procedure involves the insertion of the lenticule into a pocket prepared in the corneal stroma.
Both of the foregoing techniques require a material which transmits light, and which will allow for the passage of oxygen, glucose, and amino acids for the metabolic and nutritional requirements of the cornea. A lenticule freeze-lathed from human tissue, or from a material of high water content such as hydroxyethylmethylmetha-crylate, usually used at the present time for these prior art procedures. However, such materials suffer from unpredictability regarding the final shape of the lenticule, and therefore regarding the refractive correction of the surgical procedure.
Since the corneal stroma is maintained in a partially dehydrated state (REF), by the fluid barrier provided by the corneal epithelium, and the fluid pumping action provided by the corneal endothelium, the lenticule material is also subject to dehydration, which is not totally predictable.
In addition, the initial cutting of the presently used corneal donor material is subject to variation depending upon the water content of the material at the time of freezing and lathing. There is, therefore, a need for a lenticule material which can be cut predictably, and which will provide a known lenticule shape regardless of minor variations in the hydration of the donor corneal tissue. There is also a need to be able to measure the optical power of the lenticule before it is sutured into the cornea.
Accordingly, a major problem which is encountered when human corneal tissue is used to form the lenticule is its unpredictability, as discussed above. Specifically, it is not presently feasible to determine the refractive power of the resulting lenticule prior to its attachment to the eye of the recipient. This problem is compounded by the fact that if a number of human corneal tissues are lathed to a particular thickness, they tend to exhibit different refractive powers. These problems lead to substantial trial and error in present-day refractive surgical procedures, often requiring multiple attempts to form a lenticule, with the correct refractive power attached to the cornea of the patient's eye.
The method of the present invention, in one of its embodiments, utilizes specially treated animal corneal tissue, obtained preferably from pigs, such as suggested, for example, in U.S. Pat. No. 4,346,482 which issued Aug. 31, 1982, in the names of Jerald L. Tennant et al. The specially treated pig corneal tissue has a much higher predictable refractive power than the human tissue when lathed to a particular thickness. Moreover, the specially treated pig corneal tissue is clearer than human corneal tissue and may be subjected to pre-testing before attachment to the eye of the patient to determine the refractive power of the tissue, so that the proper tissue may be selected for a particular recipient.
Accordingly, the present invention makes possible the creation of a bank of donor tissues having pre-established refractive powers, and which may be conveniently selected and used for refractive eye surgery. An important aspect of the invention involves the treatment of the donor tissue with a fixative agent, such as gluteraldehyde, which not only neutralizes the immune response, and cross-links the tissue to prevent swelling, but which also enables the tissues to be stored for long periods of time without deterioration. Another aspect of the invention is the preparation of the lenticule with pre-placed sutures to facilitate tee surgery and reduce distortion and astigmatism.
Accordingly, an objective of the invention is to provide a method for fabricating a lenticule for use in refractive eye surgery which is formed from readily available donor tissue, and which comprises the step of treating the tissue with a fixative agent such as gluteraldehyde, so that the tissue will not induce a rejection response of the recipient immune system, and which additionally enables the tissue to be stored for long periods of time without degradation.
Another object of the invention is to provide such a method in which the tissue can be prepared in sufficient numbers to meet implantation requirements without the need to await the availability of the donor tissues.
Another objective of the invention is to provide a method for fabricating the lenticule to a selected refractive power which may be established with a high degree of precision prior to the attachment of the lenticule to the eye of the patient.
Yet another objective of the invention is to provide a method for fabricating the lenticule which does not change shape upon change of the water content during the fabrication process or upon change of the water content of the recipient cornea, and which will maintain its clarity in the eye of the patient.